Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$27.96	11.319%	$31.1248	$31.12	$31.10	$31.10
Purchase #2	$76.83	7.444%	$82.5492	$82.55	$82.55	$82.50
Purchase #3	$194.49	9.276%	$212.5309	$212.53	$212.55	$212.50
Purchase #4	$243.87	4.153%	$253.9979	$254.00	$254.00	$254.00
Purchase #5	$117.80	4.468%	$123.0633	$123.06	$123.05	$123.10
Purchase #6	$187.41	11.804%	$209.5319	$209.53	$209.55	$209.50
Purchase #7	$50.85	11.689%	$56.7939	$56.79	$56.80	$56.80
7 purchase totals =	$899.21		$969.5919	$969.58	$969.60	$969.50